1. Field of the Invention
The present invention relates to an improved magnetic recording system having a magnetic storage layer and an associated saturable, high permeability magnetic layer, both of which are arranged in cooperative relationship with relatively movable head detection means. More particularly, the invention concerns such a system where the high permeability, saturable layer provides significantly reduced reproduce spacing loss at low head flying heights, and an improved overall sensitivity permitting increased linear or areal recording density through the use of an MR detection element within the head.
2. Description of the Related Art
Wideband, high density magnetic storage systems with flying heads are well known in the prior art. Such systems include a storage layer of hard magnetic material capable of efficiently storing magnetic flux written into and reproduced from the layer in high density configuration by a flying head of high sensitivity, such as a ferrite head, a thin film inductive head, or an MR head. In such systems, one of the major factors in achieving ever higher recording densities is the capability of eliminating or minimizing the effect of various losses that occur during the transducing operations within such systems.
One of the more significant transducing losses, usually called "spacing loss", results from the physical dimension or spacing that must occur between the magnetic storage medium and the head. It is well recognized that the effect of spacing loss is more significant during the reproduce stage of storage operations. In addition to spacing loss, signal quality is affected by poor efficiency in signal transfer, as for example, that caused by reproduce gap loss. Reproduce gap loss is generally characterized as the loss in efficiency that results from the finite length of the physical gap associated with the head during transfer operations, and is of particularly noticeable impact at shorter wavelengths.
Many attempts to reduce spacing loss and reproduce loss directly, for example by reducing flying height, have met with only partial success. Collision damage, excessive transducer wear and storage medium wear still exist as limiting factors in determining transducer flying height, with substantial transducing losses still remaining in such systems.
U.S. Pat. Nos. 4,717,592 and 4,657,819 describe two film vertical recording media incorporating a layer of soft magnetic material, to suppress thermal degradation in the one case, and to reduce magnetic anisotropy-induced signal fluctuations, in the other case.
U.S. Pat. No. 5,041,922 and a related technical paper entitled "A High Resolution Flying Magnetic Disk Recording System with Zero Reproduce Spacing Loss", presented at the June 1991 IEEE Intermag Conference, describe a technique for reducing spacing and reproduce gap losses by deposition of a soft magnetic layer upon the magnetic storage layer of a storage system. The '922 patent is assigned to the same assignee as is the present application.
In an unsaturated state, the soft magnetic layer acts as a shunt path that prevents signal flux from reaching the head. However, when a saturating bias signal is applied selectively to such a soft magnetic layer, the permeability of the saturated region is lowered to the extent that signal flux from bits of information stored in the storage layer readily permeates the saturated region. At the same time, the reluctance between the head poles and the unsaturated regions of the soft layer remains relatively low. Thus, the permeability of the saturated region is near that of air, while the adjacent unsaturated zones retain high permeability.
In effect, this results in formation of a "virtual" gap in the "keeper" layer. With the virtual gap, the signal flux from the storage layer is no longer shunted by the keeper. Instead, signal flux is directed to the pole pieces of the head through the unsaturated regions of the keeper on either side of the virtual gap. Since the unsaturated regions of the keeper are in direct contact with the storage layer, the impact of physical spacing between the virtual head structure and the storage layer is greatly reduced, if not effectively eliminated.
At that time, the sections of the keeper on either side of the virtual gap can be characterized as extensions of the core structure of the system. Thus, the addition of a keeper layer in the system might be characterized as adding a "pseudo" layer of magnetic material to the head when saturation occurs. This, in turn, results in the effective elimination of spacing losses since the head spacing, although not physically changed, can be considered as an air gap that in an "equivalent" magnetic head structure increases the reluctance of the head magnetic circuit and thereby causes a small loss in head efficiency, but does not contribute the large frequency sensitive spacing loss that previously existed. The reproduce gap losses of the system are reduced, as well, through reduction in the effective length of the physical gap of the head.
A publication titled "Magnetic Recording Media Employing Soft Magnetic Material" was published Jul. 8, 1993 under International Publication No. WO 93/12928, from International Application No. PCT/U.S. 92/10485 dated Dec. 7, 1992, assigned to Connor Peripherals, Inc. The Connor application discloses and claims an improvement in a system such as that described in the '922 patent through use of a non-magnetic layer located between the storage layer of the system and the keeper layer.
The purpose of the non-magnetic layer in the Connor application is to interrupt magnetic exchange coupling between the recording layer and the soft magnetic layer of the system. It is believed the use of a layer such as that proposed by the Connor application clearly falls within the purview of the '922 patent. For example, see lines 7-10 of column 7 of the patent wherein it is disclosed that durable overcoats, or conducting coats, may be used in conjunction with the recording layer.
Indeed, such an isolation layer might well occur inherently in such a structure due to oxidation of the magnetic layers such as might occur between processing stages, during fabrication of the layered system. Moreover, one of the co-inventors of the present application is also a co-inventor with respect to the '922 patent. Since issuance of the '922 patent he has conducted additional investigation to evaluate possible benefit of using a separation layer in a structure such as that disclosed in the '922 patent. That investigation was not conclusive. However, it must be noted that the use of break layers for the purpose of reducing molecular and atomic migration across active layer boundaries is acknowledged to be a well recognized technique in the prior art, long prior to the filing date of the '922 patent.
A U.S. Patent Application titled Two-Gap Magnetic Read/Write Head, assigned to the same assignee as is the present application, by Beverley R. Gooch and George Varian was filed on the same day as the present application, disclosing an improved magnetic storage system including a saturable keeper layer associated with the magnetic recording layer and further including an improved two-gap inductive head which eliminates the need for separate read and write heads within the system.
While inductive heads used in connection with keepered disk technology are believed to represent useful gains in recording technology, and particularly in increased recording density, certain limitations exist that impede their use for the achievement of very high recording density, as measured by current standards. Since the output voltage of inductive heads is a function of disk velocity and the number of turns on the head, as recording densities increase, the operating frequency also increases, and hence noise increases. Because of resonant effects and head noise factors, the number of turns that can be placed upon a head is limited. This, in turn, limits the signal to noise performance that can be attained from an inductive head such as a ferrite head, and that factor eventually limits the potential recording density.